Development of soy protein concentrate/hemp fiber-based biocomposite foams: Effects of alkaline treatment and poly(lactic acid) coating

Abstract

Petroleum-based foams are used in packaging applications where thermal insulation and shock absorption are needed. However, their associated environmental problems motivate the development of bio-based alternatives. Here, biocomposite foams were prepared using soy protein concentrate (SPC) and alkali-treated hemp fibers. The hemp fibers were treated with 6% NaOH to remove non-cellulose components. The foams were coated by dipping in a poly(lactic acid) (PLA) solution. A concentration of 4% PLA was determined to be optimal for the coating. The mechanical and water barrier properties of the PLA-coated foams were evaluated. The compression modulus, compression strength, and bulk density of the PLA-coated foams were 1045.7 kPa, 2022.5 kPa, and 118.6 mg/mL, respectively, being significantly higher than those of the uncoated foams (404.0 kPa, 590.7 kPa, and 69.4 mg/mL). The moisture uptake and water uptake of the PLA-coated foams were significantly decreased by the coating procedure, indicating 16.2% and 138.3%, respectively. By contrast, the uncoated foams had a moisture uptake and water uptake of 31.8% and 1399.3%, respectively. The observed improvement in mechanical and water barrier properties is likely due to the hydrophobic nature of PLA. • Biobased foams were made using soy protein concentrate and hemp fibers. • The hemp fibers were treated with 6% NaOH to remove non-cellulose components. • The foams were coated with 4% polylactic acid (PLA). • The PLA-coated foams showed enhanced mechanical properties and water resistance.